Injector for liquid medicine

ABSTRACT

An injector for liquid medicine comprises a cylindrical body  1 , first and second gasket  2, 3  contained in a lumen of cylindrical body  1 . The cylindrical body  1  is provided with a fluid inlet  13  and a fluid outlet  14  in opposite sides of the cylindrical body  1  with respect to the longitudinal axis thereof. Second gasket  3  is spaced from the first gasket  2  to form a fluid chamber  4  between them. The first gasket  2  is adapted to be moved by sliding along the inner wall of the cylindrical body  1  from a first position to the distal end  11  of cylindrical body  1  via a second position. The fluid inlet  13  is opened at a position closer to the distal end  11  of the cylindrical body  1  than the outlet  14  is. The first gasket  2  is stopped at a second position where the fluid chamber  4  is communicated with the fluid outlet  14  but prevented from fluid-communication with the fluid inlet  13.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an injector for liquid medicine and,more particularly, an injector which enables to continually administer alittle dose of a liquid medicine after priming. The injector of thepresent invention is useful for administration of an additional medicinein midstream of administration of one medicine and for administration ofa medicine which may cause infection of an operator during mixedadministration of different medicines such as antitumor agents.

2. Background Art

When performing administration of a liquid medicine with an infusion setor a catheter, it is frequently necessary to administer another medicinein midstream of administration. Such operations are required, forexample, in administration of contrast media, hormone preparations,peptide preparations, antitumor agents, vitamin preparations, etc. Thisis generally done using a prefilled syringe, i.e., a syringe with aliquid medicine previously charged therein.

So far, such mixed administration has been carried out using a three-waystopcock or a Y-shaped tube to change over route of administration.

However, use of the three-way stopcock or Y-shaped tube may causeleakage of the charged medicine at the time of connection of theprefilled syringe or priming operation. In particular, in case ofmedicines such as antitumor agents which are high in carcinogen, theleakage of such a medicine may causes health problems of the operator.Further, the administration of a little dose of expensive medicine isdifficult to operate and makes it difficult to perform effectiveadministration since the medicine may be diluted with other medicine. Inaddition, there is a problem such that the medicine is remained in routeof administration.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide aninjector for liquid medicine which is easy to operate, makes it possibleto continually administer a little dose of a liquid medicine differentfrom a first liquid medicine during administration of the first liquidmedicine.

According to one aspect of the present invention, there is provided aninjector for liquid medicine comprising:

-   -   a cylindrical body having an opening at each end thereof and        provided with a fluid inlet and a fluid outlet in opposite sides        of the cylindrical body with respect to the longitudinal axis        thereof, said inlet and outlet being respectively communicated        with a lumen of the cylindrical body, said inlet being located        at a position closer to the distal end of the cylindrical body        than the fluid outlet is; and    -   first and second gaskets fluid-tightly and slidably arranged in        the lumen of said cylindrical body and adapted to be moved along        an inner wall of said cylindrical body, said first and second        gaskets being spaced from one another to form a fluid chamber        between them, said fluid chamber being filled with a liquid        medicine;    -   said first gasket being slidable from a first position where the        fluid inlet and outlet are communicated with one another, to a        distal end of the cylindrical body via a second position where        said fluid chamber is prevented from fluid-communication with        the fluid inlet but communicated with the fluid outlet to inject        the liquid medicine in the fluid chamber through the fluid        outlet.

The first gasket has sealing portions adjacent to each end thereof andis provided with a flow path in a central portion thereof. The fluidinlet and outlet are communicated with one another through the flow pathat the first position. The cylindrical body may be provided with meansfor stopping the sliding movement of the first gasket at the secondposition. In this case, the second gasket may have sealing portions oneach end thereof and is provided with a flow path between the sealingportions to allow the user to inject the medicine through the fluidinlet after administration of the medicine contained in the fluidchamber. In that case, the second gasket should allow the fluid inlet ofthe cylindrical body to be communicated with the fluid outlet throughthe flow path thereof when the first gasket is moved to the distal endof cylindrical body along with the second gasket. The flow path may bein the form of a circumferential groove or channel formed betweensealing portions or in the form of a through-hole passing through thegasket.

The cylindrical body may be provided at a proximal end thereof with aplunger for pushing the second gasket toward the distal end of thecylindrical body. The stop means may be plural ribs extending from theposition adapted to be engaged with the first gasket to the distal endof the cylindrical body along the inner wall of the cylindrical body.

In a preferred embodiment of the present invention, the first gasket hassealing portions adjacent to each end thereof and a flow path formedbetween the sealing portions. The first gasket is adapted to be movedfrom a first position where it allows the fluid inlet of the cylindricalbody to be communicated with the fluid outlet through the flow path. Atleast one of the proximal end of first gasket and the distal end of thesecond gasket may be provided with a cylindrical protrusion having anouter diameter smaller than an inner diameter of the cylindrical bodyand being protruded into the fluid chamber, so that the first gasketand/or second gasket allows the fluid inlet to be communicated with thefluid outlet through an annular gap formed between the cylindrical bodyand the protrusion when the first gasket is moved to the distal end ofcylindrical body. The flow path may be in the form of a circumferentialgroove or channel formed between sealing portions or in the form of athrough-hole passing through the gasket perpendicular to the gasket. Thecylindrical body may be provided at a proximal end thereof with aplunger for pushing the second gasket toward the distal end of thecylindrical body.

In another embodiment of the present invention, the injector furtherincludes a third gasket located between the first and second gaskets.The third gasket is brought into contact with the proximal end of thefirst gasket but spaced from the second gasket to form a fluid chamberbetween them. At least one of the proximal end of first gasket and thedistal end of the third gasket is provided with a cylindrical protrusionhaving an outer diameter smaller than an inner diameter of thecylindrical body and being protruded into the fluid chamber. Similarly,at least one of the proximal end of third gasket and the distal end ofthe second gasket is provided with a cylindrical protrusion having anouter diameter smaller than an inner diameter of the cylindrical bodyand being protruded into the fluid chamber.

When the first gasket is present in the first position, the first andthird gaskets allow the fluid inlet to be fluid-communicated with thefluid outlet through the annular gap formed between the protrusionsthereof and the inner wall of the cylindrical body. When the firstgasket is moved to the distal end of the cylindrical body, the secondgasket is in contact with the third gasket and the second and thirdgaskets allow the fluid inlet to be communicated with the fluid outletthrough the annular gap formed between the protrusions thereof and theinner wall of the cylindrical body.

The injector of the present invention can be used in combination with asyringe for injection of contrast media for myocardial scintigraphy intoa vein, or for infusion of hormone preparation into a dialysis circuitfor treatment of renal anemia, or for administration of peptidepreparations for treatment of osteoporosis, or administration ofantitumor agents, or the like. Further, the injector of the presentinvention can be used, in combination with infusion solution bag orbottle connected thereto with tubing, for administration of vitaminpreparation just before infusion of a high-calorie infusion solution toprevent Maillard reaction.

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal section illustrating an embodiment of aninjector of the present invention;

FIGS. 2 through 5 illustrate sequential steps of operation of theinjector shown in FIG. 1;

FIG. 6 is a longitudinal section illustrating another embodiment of aninjector of the present invention;

FIGS. 7 through 9 illustrate sequential steps of operation of theinjector shown in FIG. 6;

FIG. 10 is a longitudinal section illustrating another embodiment of aninjector of the present invention;

FIGS. 11 through 13 illustrate sequential steps of operation of theinjector shown in FIG. 10;

DETAILED DESCRIPTION OF THE INVENTION

As illustrated in FIGS. 1, 6 and 10, an injector of the presentinvention generally comprises a cylindrical body 1, a first gasket 2contained in a lumen of the cylindrical body 1 and arranged on the sideof the distal end thereof, and a second gasket 3 contained in the lumenof the cylindrical body 1 and arranged on the side of the proximal endthereof. The cylindrical body 1 is provided with a fluid inlet 13 and afluid outlet 14 in opposite sides of the cylindrical body 1 with respectto the longitudinal axis thereof. The second gasket 3 is spaced from thefirst gasket 2 to form a fluid chamber 4 between them, which is filledwith a liquid medicine. The first gasket 2 is adapted to be moved bysliding along the inner wall of the cylindrical body 1 from a firstposition to a distal end of the cylindrical body 1 via a secondposition. At the first position, the first gasket 2 allows the fluidinlet 13 to be fluid-communicated with the fluid outlet 14 through theflow path 22 provided in the first gasket 2. At the second position, thefirst gasket 2 allows the fluid chamber 4 to be prevented fromfluid-communication with the fluid inlet 13 but to be fluid-communicatedwith the fluid outlet 14. The fluid inlet 13 is open to the lumen of thecylindrical body 1 at a position closer to the distal end 11 of thecylindrical body 1 than the fluid outlet 14 is. When the first gasket 2is moved to the second position where the fluid chamber 4 iscommunicated with the fluid outlet 14 but prevented fromfluid-communication with the fluid inlet 13, the liquid medicine in thefluid chamber 4 is discharged through the fluid outlet 14.

Referring now to FIG. 1, the liquid medicine injector of the firstembodiment of the present invention comprises the cylindrical body 1 andthe first and second gaskets 2, 3 arranged therein. The cylindrical body1 is provided with the fluid inlet 13 and the fluid outlet 14 inopposite sides of the cylindrical body 1 with respect to thelongitudinal axis thereof. The second gasket 3 is spaced from the firstgasket 2 to form the fluid chamber 4 between them. The first gasket 2 isprovided with the flow path 22 in a central part thereof and is movablefrom the first position where the flow path 22 allows the fluid inlet 13to be communicated with the fluid outlet 14, to the distal end 11 of thecylindrical body 1. The fluid inlet 13 is open to the lumen of thecylindrical body 1 at a position closer to the distal end 11 of thecylindrical body 11 than the fluid outlet 14 is. The first gasket 2 isadapted to be stopped at the second position where the fluid chamber 4is communicated with the fluid outlet 14 and but not fluid-communicatedwith the fluid inlet 13.

The cylindrical body 1 is opened at both ends 11 and 12 and providedwith the fluid inlet 13 and the fluid outlet 14 in opposite sides of thecylindrical body 1 with respect to the longitudinal axis thereof. Thefluid inlet 13 is open to the lumen of the cylindrical body 1 at aposition which is closer to the distal end of the cylindrical body 1than the fluid outlet 14 is. Two gaskets 2 and 3 are liquid-tightlyarranged in the lumen of the cylindrical body 1 and are slidable alongthe lumen of the cylindrical body 1. A space formed between the firstand second gaskets 2 and 3 serves as a fluid chamber 4, which is filledwith a liquid medicine.

The first gasket 2 on the side of the distal end 11 of the cylindricalbody 1 has sealing portions 21 adjacent to the end surfaces thereof andis provided with a flow path 22 at the central portion thereof. The flowpath 22 may be in the form of a circumferential groove or channel 22formed between sealing portions 21 or in the form of a through-hole (notshown) which crosses the first gasket 2. The first gasket 2 is movablefrom the first position where the fluid inlet 13 of the cylindrical body1 is communicated with outlet 14 through the flow path 22, to the distalend 11 of cylindrical body 1. At the distal end 11 of the cylindricalbody 1 there is provided an annular projection 16 inwardly extendingfrom the distal end 11 to prevent the first gasket 2 from being movedbeyond the distal end 11. The first gasket 2, when being moved towardthe distal end 11 of the cylindrical body 1, is adapted to be stopped atthe second position where the fluid chamber 4 is communicated with thefluid outlet 14 and but prevented from fluid-communication with thefluid inlet 13. To this end, the cylindrical body 1 is provided at thedistal end thereof with means for stopping the first gasket 2. The stopmeans may be one or more longitudinal ribs 15 provided on the interiorof the cylindrical body 1 and extending from the position being adaptedto be engaged with the first gasket 2 to the distal end 11, as shown inFIG. 1. Alternatively, the stop means may be a stop member (not shown)removably fitted in the lumen of the cylindrical body 1 through theopening of the cylindrical body 1. For example, the stop member may be acap-like member having a structure similar to that of a plunger 5mentioned below and having a fitting portion with an outer diametersmaller than that of the annular projection 16.

The second gasket 3 on the side of the proximal end 12 may be a gasketwith no flow path. Preferably, the second gasket 3 is a gasket havingsealing portions 31 at both ends thereof and is provided with a flowpath 32 at a central portion thereof to allow the user to inject aliquid medicine through the fluid inlet 13 after injection of the liquidmedicine contained in the fluid chamber 4. In this case, it is necessaryto allow the fluid inlet 13 to be communicated with the fluid outlet 14through the flow path 32 of the second gasket 3 when the first gasket 2is moved to the distal end 11 of the cylindrical body 1 under thecondition that the first gasket 2 is brought into contact with thesecond gasket 3.

The cylindrical body 1 may be provided at the proximal end thereof witha plunger 5 for pushing the second gasket 3 toward the distal end 11.The plunger 5 may be a cap-like member as illustrated in FIG. 1. In thisembodiment, the plunger 5 comprises a cylindrical engaging portion 51slidably fitted on the outer wall of the cylindrical body 1 and acylindrical protrusion 52 adapted to come into contact with the secondgasket 3. The plunger 5 is adapted to be moved from a position where anannular rib 511 of the engaging portion 51 engages with an annulargroove 17 of the cylindrical body 1, to a position where an annular rib511 of the engaging portion 51 engages with a stepped portion 18 of thecylindrical body 1.

Use of the medicine injector shown in FIG. 1 will be explained belowwith reference to FIGS. 2 to 5 which illustrate a sequence of operationfor injecting contrast media into a vein.

There is prepared a liquid medicine injector I with a fluid chamber 4filled with a dose of contrast media (not illustrated). A needle, e.g.,a winged catheter, is connected to the fluid outlet 14 of the injectorI. At that time, the first gasket 2 is located at a first position wherethe flow path 22 allows the fluid inlet 13 to be communicated with thefluid outlet 14. Then, the fluid inlet 13 of the injector I is fittedwith a tip 6 of a syringe S filled with a physiologic saline (not shown,herein after referred to as “saline”), as illustrated in FIG. 2. Bypressing a plunger 7 of the syringe S, the saline in the syringe S isejected forcefully through the winged catheter via the fluid inlet 13,flow path 22 and fluid outlet 14, so that the flow channel for thecontrast media is washed with the saline. This operation is called as“priming”.

After priming, the winged catheter is inserted in a vein of a patient.The plunger 5 of the injector I is then pressed to move the secondgasket 3, fluid chamber 4 and first gasket 2 toward the distal end ofthe injector I and stopped at a second position where the fluid chamber4 is communicated with the fluid outlet 14 but prevented from thefluid-communication with the fluid inlet 13. By further pressing theplunger 5, the contrast media in the fluid chamber 4 is injected throughthe winged catheter into the vein via the fluid outlet 14 (see FIG. 3).When the fluid chamber 4 is emptied, the first and second gaskets 2 and3 are brought into contact with one another and then moved togethertoward the distal end of the cylindrical body 1 until the first gasket 2is engaged with the annular projection 16. At that time, the fluid inlet13 is communicated with the fluid outlet 14 through the flow path 32 ofthe second gasket 3, as illustrated in FIG. 4. By pressing the plunger 7of the syringe S, the saline passes through the fluid inlet 13, flowpath 22, fluid outlet 14 and winged catheter so that the contrast mediumremained in the fluid outlet 14 and the winged catheter is injected intothe vein (cf. FIG. 5).

Referring now to FIG. 6, there is shown another embodiment of the liquidmedicine injector which comprises a cylindrical body 1 and first andsecond gaskets 2, 3 which are fluid-tightly and movably fitted into thecylindrical body 1 and spaced from one another to form a fluid chamber 4between them.

The first and second gaskets 2, 3 are fluid-tightly and movably fittedinto the cylindrical body 1 and spaced from one another to form a fluidchamber 4 between them.

The cylindrical body 1 is opened at both ends thereof and provided inopposite faces thereof with a fluid inlet 13 and a fluid outlet 14 eachhaving an opening communicated with an interior of the cylindrical body1 and an axis perpendicular to the longitudinal axis of the cylindricalbody 1. The fluid inlet 13 is open to the lumen of the cylindrical body1 at a position closer to the distal end of the cylindrical body 1 thanthe fluid outlet 14 is. The first gasket 2 has a flow path 22 formedbetween the sealing portions 21, 23 and being movable from a firstposition where the fluid inlet 13 and outlet 14 are fluid-communicatedthrough the flow path 22 to the distal end 11 of the cylindrical body 1.To the proximal end of the first gasket 2 and the distal end of thesecond gasket 3, there are provided respectively with a cylindricalprotrusion 24, 33 having an outer diameter smaller than an innerdiameter of the cylindrical body 1. The fluid inlet 13 is open to thelumen of the cylindrical body 1 at a position closer to the distal end11 of the cylindrical body 1 than the fluid outlet 14 is. When the firstgasket is moved to the distal end 11 of the cylindrical body 1, thefluid inlet 13 and outlet 14 are communicated with one another throughthe gaps between the inner wall of the cylindrical body 1 and thecylindrical protrusion 24, 33. The cylindrical body 1 is furtherprovided with an annular projection 16 at the distal end thereof toprevent the first gasket 13 from being moved beyond the distal end 11.

The first gasket 2, which is located on the distal side of thecylindrical body 1, is a disk-shaped member having sealing portions 21,23 adjacent to each end thereof and a flow path 22 formed between thesealing portions 21, 23. In this embodiment, the flow path 22 is anannular groove or channel formed in the circumference of the firstgasket 2, but it may be a linear hole (not shown) passing through thefirst gasket 2. The first gasket 2 is provided on the proximal endthereof with a cylindrical protrusion 24 having an outer diametersmaller than an inner diameter of the cylindrical body 1.

The first gasket 2 is adapted to be moved from a first position where itallows the fluid inlet 13 to be communicated with the fluid outlet 14through the flow path 22, to the distal end 11 of cylindrical body 1 viaa second position where the fluid chamber 4 is communicated with thefluid outlet 14 and but prevented from the fluid-communication with thefluid inlet 13. The first gasket 2 is automatically stopped at thesecond position.

The second gasket 3, which is located on the proximal side of thecylindrical body 1, has a configuration similar to that of the firstgasket 2 and has a cylindrical protrusion 34 having an outer diametersmaller than an inner diameter of the cylindrical body 1. In thisembodiment, the cylindrical protrusions 24, 33 are provided on both thefirst and second gaskets, but may be provided on either first gasket 2or second gasket 3. Thus, one of the first and second gaskets isprovided with a cylindrical protrusion 24 or 33, the other gasket may bea gasket with a conventional configuration.

In order to facilitate the operation of the injector, the cylindricalbody 1 may be provided at its proximal end with a plunger 5 for pushingthe second gasket 3 toward the distal end 11. It is preferred to use aplunger 5 in the form of a cap-like member as illustrated in FIG. 6. Theplunger 5 has a cylindrical engaging portion 51 fitted on the outer wallof the cylindrical body 1 and a cylindrical protrusion 52 which comesinto contact with the second gasket 3. The plunger 5 is movable from afirst position where an annular rib 511 of the engaging portion 51engages with an annular groove 17 of the cylindrical body 1, to a secondposition where an annular rib 511 of the engaging portion 51 engageswith a stepped portion 18 of the cylindrical body 1.

An example of how the medicine injector of FIG. 6 is used will be madewith reference to FIGS. 7 to 9 which illustrate a sequence of operationfor injecting contrast media into a vein.

Firstly, a needle, e.g., a winged catheter, is connected to the fluidoutlet 14 of a liquid medicine injector I with a fluid chamber 4 filledwith a dose of contrast media (not illustrated). At that time, the firstgasket 2 is located at the first position where it allows the fluidinlet 13 to be communicated with the fluid outlet 14 through the flowpath 22. Then, the injector I is fitted with a syringe S containingsaline, by fitting a tip 6 of the syringe S in the fluid inlet 13 of theinjector I, as illustrated in FIG. 2. By pressing a plunger 7 of thesyringe S, the saline in the syringe S is ejected forcefully through thewinged catheter via the fluid inlet 13, flow path 22 and fluid outlet14, so that the whole length of the flow channel for the contrast mediais washed with the saline.

After completing the above priming, the winged catheter is inserted in avein of a patient. The plunger 5 of the injector I is then pressed tomove the second gasket 3, fluid chamber 4 and first gasket 2 toward thedistal end of the injector I until the first gasket 2 is stopped at thesecond position where the fluid chamber 4 is communicated with the fluidoutlet 14 through a gap between the protrusion 24 and inner surface ofthe cylindrical body 1 but prevented from the fluid-communication withthe fluid inlet 13, as illustrated in FIG. 8. Thus, the contrast mediain the fluid chamber 4 is injected through the winged catheter into thevein by further pressing the plunger 5. As soon as the fluid chamber 4is emptied, the second gasket 3 is brought into contact with the firstgasket 2 and then moved together toward the distal end 11 of thecylindrical body 1 until the first gasket 2 reaches to the distal end 11of the cylindrical body 1. At that time, the fluid inlet 13 iscommunicated with the fluid outlet 14 through the gap between thecylindrical protrusion 24, 33 and the inner wall of the cylindrical body1, as illustrated in FIG. 9. By pressing the plunger 7 of the syringe S,the saline is injected into the vein through the fluid inlet 13, gapbetween the protrusion 24 and inner wall of the cylindrical body 1,fluid outlet 14 and winged catheter. Thus, the contrast media present inthe gap, the fluid outlet 14 and winged catheter is injected into thevein together with the saline.

The liquid medicine injector shown in FIG. 10 comprises a cylindricalbody 1 and first, second and third gaskets 2, 3 and 9 which arefluid-tightly and movably fitted into cylindrical body 1. The thirdgasket 9 located between the first and second gaskets 2 and 3 is broughtinto contact with the first gasket 2 but spaced from the second gasket 3to form a fluid chamber 4 between the second gasket 2 and the thirdgasket 9. The first and second gaskets 2, 3 have the same configurationsas those of embodiment of FIG. 6, while the third gasket 9 is providedat each circular end with a cylindrical protrusion 91, 92 having adiameter smaller than the inner diameter of the cylindrical body 1.Preferably, the diameter of cylindrical protrusion 91, 92 isapproximately equal to that of the cylindrical protrusions 24 and 33 ofthe first and second gaskets 2 and 3.

The first gasket 2 is adapted to be moved together with the third gasket9 from a first position to the distal end 11 of cylindrical body 1 via asecond position. At the first position, the first and third gaskets 2and 9 allow the fluid inlet 13 to be communicated with the fluid outlet14 through the annular gaps formed between their protrusions 24, 91 andthe inner wall of the cylindrical body 1. At the second position, thethird gasket 9 allows the fluid chamber 4 to be prevented from thefluid-communication with the fluid inlet 13 but communicated with thefluid outlet 14 through the annular gaps formed between the protrusion91 and the inner wall of the cylindrical body 1.

The cylindrical body 1 is opened at both ends 11, 12 thereof andprovided in opposite faces thereof with a fluid inlet 13 and a fluidoutlet 14 each having an opening communicated with a lumen of thecylindrical body 1 and an axis perpendicular to the longitudinal axis ofthe cylindrical body 1. Since the remaining parts of the injector arethe same as that of the injector shown in FIG. 6, there would be no needto provide detailed description thereof.

An example of how the medicine injector of FIG. 10 is used will be madewith reference to FIGS. 11 to 13 which illustrate a sequence ofoperation for injecting contrast media into a vein.

Firstly, a liquid medicine injector I with a fluid chamber 4 filled witha dose of contrast media (not illustrated) is prepared and fitted with aneedle, e.g., a winged catheter, by fitting it into the fluid outlet 14thereof. At that time, the first gasket 2 is located at the firstposition where it allows the fluid inlet 13 to be communicated with thefluid outlet 14 through the gaps formed between the protrusions 24, 91and the inner wall of the cylindrical body 1. Then, the injector I isfitted with a syringe S containing saline, by fitting a tip 6 of thesyringe S in the fluid inlet 13 of the injector I, as illustrated inFIG. 11. By pressing a plunger 7 of the syringe S, the saline in thesyringe S is ejected forcefully through the winged catheter via thefluid inlet 13, gaps and outlet 14, so that the whole length of the flowchannel for the contrast media is washed with the saline.

After completing the above priming operation, the winged catheter isinserted in a vein of a patient. The plunger 5 of the injector I is thenpressed to move the second gasket 3, fluid chamber 4, third gasket 9 andfirst gasket 2 toward the distal end of the injector I until the firstgasket 2 is stopped at the second position where the fluid chamber 4 iscommunicated with the fluid outlet 14 through the gap between theprotrusion 92 and the inner surface of the cylindrical body 1 butprevented from the fluid-communication with the fluid inlet 13, asillustrated in FIG. 12. By further pressing the plunger 5 under such acondition, the contrast media in the fluid chamber 4 is injected throughthe winged catheter into the vein. As soon as the fluid chamber 4 isemptied, the second gasket 3 is brought into contact with the thirdgasket 9 and then moved together with the first and third gaskets 2 and9 toward the distal end 11 of the cylindrical body 1 until the firstgasket 2 reaches to the distal end 11 of the cylindrical body 1. At thattime, the fluid inlet 13 is communicated with the fluid outlet 14through the gaps between the cylindrical protrusion 92, 33 and the innerwall of the cylindrical body 1, as illustrated in FIG. 13. By pressingthe plunger 7 of the syringe S, the saline is injected into the veinthrough the fluid inlet 13, gaps between the protrusion 92, 33 and innerwall of the cylindrical body 1, fluid outlet 14 and winged catheter.Thus, the contrast media present in the flow path between the fluidoutlet 14 and winged catheter is injected into the vein together withthe saline.

As will be understood from the above, since the administration mode canbe changed only by simple pushing operation of the plunger, the injectorof the present invention is easy to operate. Further, it is possible toadminister different medicines sequentially. This is convenient foradministration of a small dose of an expensive medicine. Afteradministration of a first medicine, the subsequent second medicine isscarcely mixed with the previous first medicine. Thus, there is nodilution of the subsequent medicine during administration, which in turnmakes it possible to perform effective administration. In addition, theexpensive medicine remained in route of administration can be injectedinto the site by injecting the first inexpensive medicine thereafter.This makes it possible to minimize loss of the expensive medicine.

1. An injector for liquid medicines comprising: a cylindrical bodyhaving an opening at proximal and distal ends thereof and provided witha fluid inlet and a fluid outlet on opposite sides of the cylindricalbody, axes of the fluid inlet and fluid outlet being substantiallyperpendicular to axes of the openings of the proximal and distal ends ofthe cylindrical body, said inlet and said outlet respectivelycommunicating with a lumen of the cylindrical body, said inlet openingat a position closer to the distal end of the cylindrical body thanwhere the fluid outlet opens; and a plurality of gaskets displacedrelative to each other and being fluid-tight and slidably arranged inthe lumen of said cylindrical body and adapted to be moved along aninner wall of said cylindrical body, said plurality of gaskets formingat least one fluid chamber therebetween, said at least one fluid chamberbeing filled with a liquid medicine; a first gasket of said plurality ofgaskets being provided with a flow path and being slidable from a firstposition where the fluid inlet and outlet are communicated with oneanother through the flow path of the first gasket, to the distal end ofthe cylindrical body via a second position where said at least one fluidchamber is prevented from fluid-communication with the fluid inlet butcommunicating with the fluid outlet to inject the liquid medicine in thefluid chamber through the fluid outlet.
 2. The injector according toclaim 1, wherein said first gasket has sealing portions adjacent to eachend thereof and said flow path is formed in a central portion thereof,and wherein said cylindrical body is provided with means for stoppingthe sliding movement of the first gasket at the second position.
 3. Theinjector according to claim 2, a second gasket of said plurality ofgaskets has sealing portions on each end thereof and is provided with aflow path the sealing portions to allow the fluid inlet of thecylindrical body to communicate with the fluid outlet through the flowpath thereof when the first gasket is moved to the distal end ofcylindrical body along with the second gasket.
 4. The injector accordingto claim 2, wherein the flow path is a circumferential groove or channelformed between sealing portions.
 5. The injector according to claim 2,wherein the flow path is a through-hole formed between sealing portionsand passing through the gasket.
 6. The injector according to claim 2,wherein the cylindrical body is provided at a proximal end thereof witha plunger for pushing a second gasket of said plurality of gasketstoward the distal end of the cylindrical body.
 7. The injector accordingto claim 2, wherein said stop means is a plurality of ribs extendingfrom the position being adapted to be engaged with the first gasket tothe distal end of the cylindrical body along the inner wall of thecylindrical body.
 8. The injector according to claim 1, furtherincluding a third gasket of said plurality of gaskets located betweenthe first gasket and a second gasket, said third gasket being in contactwith the proximal end of the first gasket but spaced from the secondgasket to form a fluid chamber therebetween, at least one of a proximalend of first gasket and a distal end of the third gasket being providedwith a cylindrical projection having an outer diameter smaller than aninner diameter of the cylindrical body/projecting into the fluidchamber, said first and third gaskets being adapted to allow the fluidinlet to communicate with the fluid outlet through the annular gapsformed between the projections thereof and the inner wall of thecylindrical body when the first gasket is present in the first position,said second gasket being adapted to be brought into contact with thethird gasket so that the second and third gaskets allow the fluid inletto communicate with the fluid outlet through the annular gaps formedbetween the projections thereof and the inner wall of the cylindricalbody when said first gasket is moved to the distal end of thecylindrical body.